A method of this kind is known from the marketplace. In this method, the fuel is conveyed by fuel pumps at high pressure into a fuel collecting line (rail). Injectors are connected to the fuel collecting line and these injectors inject the fuel directly into a combustion chamber assigned to the corresponding injector. In this way, a so-called stratified air/fuel mixture can be generated in the combustion chamber in specific operating states of the engine. This air/fuel mixture can, overall, be leaner than a homogeneously distributed air/fuel mixture so that an engine operated in this manner consumes comparatively little fuel.
During operation of such an internal combustion engine, and for a cold engine, the problem is present that a portion of the fuel condenses on the cold combustion chamber walls or is deposited directly as liquid on the wall. Without corresponding countermeasures, for example, when starting a cold engine, the air/fuel mixture, which is present in the combustion chamber, would be so lean that it could not be ignited.
This is countered in that basically for a cold internal combustion engine, more fuel is injected into the combustion chamber of the engine than is required in normal operation for forming an ignitable and combustible air/fuel mixture. The fuel quantity, which arrives in the combustion chamber of the engine when the engine is cold, can, in this way, easily be five to thirty times the fuel quantity required in normal operation.
This excessive fuel, which condenses on the combustion chamber walls or deposits directly as liquid, is, for the most part, discharged uncombusted into the exhaust-gas system of the engine. In an operation of the engine of this kind, very high hydrocarbon emissions are generated. These high hydrocarbon emissions during the start phase, restart phase and warm-up phase contribute significantly to the total exhaust-gas emissions during the operation of the engine. A reduction of these emissions can therefore significantly reduce the total emissions of the engine. At the same time, the introduced additional quantity contributes to an increased fuel consumption in the cold start phase.
An internal combustion engine is known from U.S. Pat. No. 6,390,059 which can be started in stratified operation. This means that an ignitable and combustible mixture is only present in the region of the spark plug; whereas, in the remaining combustion chamber and especially also in the vicinity of the cold cylinder walls, an extremely lean mixture or even only pure air is present. In this way, damaging exhaust-gas emissions can be reduced during the start phase of the engine.
In order to start an internal combustion engine in stratified operation, a mixture cloud separated sharply from the surrounding air must arise in the charge stratification. For this purpose, a very special injector is, for example, necessary. This injector is, however, complex and expensive and cannot be retrofitted.
An additional problem occurs especially when a cold engine is operated only for a short time after a start or does not become warm for other reasons. In the next start of the engine, so-called spark fouling can occur primarily for very cold temperatures (<00) because of the large injected fuel quantities. This is understood to mean that the spark plug of a combustion chamber of the engine as well as the entire combustion chamber becomes so damp because of the large introduced fuel quantity that ignition problems occur and, in the worst case, a reliable start of the engine is no longer possible.